One form of a method of centeredly clamping a motor vehicle wheel on a main shaft of a balancing machine for balancing the wheel provides that the wheel is clamped, with an axially directed clamping force, on a centering cone member which is appropriately mounted on the shaft of the machine. A biasing force is directed axially in opposite relationship with respect to the clamping force, and is operable to act between the wheel and the centering cone member. In the apparatus for implementing such a method the apparatus, besides the centering cone member arranged on the main shaft coaxially with respect thereto, comprises clamping means which are actuated for movement axially with respect to the main shaft by an electric motor, for selectively clamping and releasing the wheel in relation to the centering cone member. The biasing force directed in opposite relationship to the clamping force is produced for example by means of a spring. Reference may be made in this respect to U.S. Pat. No. 5,615,574, corresponding to EP 0 550 816 B1 and DE 42 00 380 C2.
The wheel is clamped to the main shaft of the balancing machine and released therefrom by virtue of axial movements of a pull rod which is passed through an axial bore in the main shaft. The axial movement of the pull rod which is used to clamp and release the wheel is produced by the above-mentioned electric motor which constitutes a rotary drive, the rotary movement of which is converted into a linear movement of the pull rod.
In order to achieve adequate centering of the motor vehicle wheel on the main shaft, it is necessary to lift the motor vehicle wheel and push it up over the tapering clamping surface of the centering cone member. The force which is required for that purpose has to be furnished by an operator or by an additional mechanical wheel-positioning unit which is provided with a lifting drive. There is however the danger in that respect that the wheel is not exactly fitted with the central bore thereof on to the centering cone member, before the wheel is clamped in position by operation of the clamping means. That can give rise to centering errors which can consequentially result in falsification of unbalance measurement values ascertained in a measuring run of the unbalance measuring apparatus. Centering errors of 1/10 mm already cause serious deviations from the actual correct unbalance values.